1. Field of the Invention
The present invention relates to a system for developing photo-resist material used as a recording medium of an optical recording means such as an optical recording disc.
2. Description of the Prior Art
In recent years, optical recording systems have become popularly used for recording various information such as video signals and digital audio signals.
In a video disc player system or a compact digital audio disc player system, a laser beam is focused on the surface of a rotating disc having an optical pattern such as a series of pits or projections which represents recorded information. A reflection beam from the optical pattern on the disc is received by a photoelectric transducer which produces an electric output of a playback signal corresponding to the recorded information.
A master disc of this system comprises a glass base whose surface is polished, and a layer of a photoresist material formed thereon.
At the time of recording a recording laser beam, which is modulated in accordance with a signal indicative of the information to be recorded, is focused on the photo-resist layer of the master disc which is rotated at a predetermined high speed and which simultaneously is slowly translated along a radial axis thereof. Thus, the information is recorded along a spiral track on the photo-resist layer. After passing through such an exposure process, the photo-resist material of the disc is treated in a developing process, where the exposed portions of the photo-resist material are removed by a developing solution to engrave a series of pits representing the recording information.
Using the thus produced master disc, playback discs are manufactured in large quantities in much the same manner as conventional analog records.
Since the size of the pits formed by the developing process (i.e., the depth and width of the pits) is a factor which directly affects the precision of the playback operation, pit information must be controlled to be within a predetermined range of tolerance.
In order to control the size of the pits, it is necessary to adjust the time of developing, that is, the time duration of chemical reaction on the exposed portions of the photo-resist material. The speed of the chemical reaction, however, is affected by various parameter such as the degree of exposure, the density and the temperature of the developing solution, and so on.
In the case of piror art developing systems, the advancement of the chemical reaction is not monitored, and hence there is a problem that the size of the pits tends to vary from one disc to another.